The present invention relates to a shift shock alleviating system for an automatic transmission, and more particularly to an electro-hydraulic control system for controlling a change of gears of a multi-ratio automatic transmission.
U.S. Pat. No. 4,502,354 issued to Suzuki et al, discloses a hydraulic pressure control system for an automatic transmission. In this known control system, a servo actuating hydraulic pressure (line pressure) is temporally reduced during a change of gears so that a pressure applied via a gear shift valve to a servo for a shifting frictional element increases gradually during the change of gears. This measure is found to be effective in reducing a shift shock during the change of gears, but it is not effective at all in reducing a shock occurring due to a change in a transmission output torque at the ending of an inertia phase of the change of gears. Another problem with this measure is that the rate of increase and the timing of increase of hydraulic fluid supplied to the shifting frictional element do not meet actual demands at the beginning of the inertia phase. This results in production of a shock at the beginning of the inertia phase.